1. In recent decades, observations of white dwarf supernovae made a significant

Question

1. In recent decades, observations of white dwarf supernovae made a significant change in our understanding of the most distant reaches of the observable universe.

a. What property of these supernovae make them useful for measuring distances?

b. What other property of these supernovae make them particularly useful for studying very distant objects??

2. List at least two pieces of evidence that supermassive black holes exist at the centers of galaxies.

3. Identify the power source that makes quasars shine.

Explanation / Answer

1a: Supernovas are luminous and last in 2-3 weeks. This property makes to see the objects at enormous distances. They outshine the galaxies that they are present. As they last long enough, astronomers can discover them in automated surveys, can measure their light curves and peak brightness can also be estimated.

1b: Supernovas are exploding starts. This occurs within a galaxy in every 100 years and is the brightest among all in the galaxy. When a star explodes, it gives out so much energy which can outshine briefly all the starts in its galaxy. To find the distance to the galaxy that has supernova, the brightness is to be observed and measured. Using the inverse square law, distance to supernova and obviously to its galaxy can be known.

2. Observations in the infrared, radio and x ray bands pierce the thick dust obscuring the center of galaxy in the optical revealed a compact and non stellar source of radiation(Let us say B) surrounded by a cluster of starts. After measuring stellar motions and radial velocities, it is possible to infer that the position of B coincides with a dark mass of 3*106 to 4*106

3. Quasars are brightest objects in the universe. The possible source that best fits the brightness of a quasar is a super massive black hole at its center. The center of a quasar, black hole, is surrounded by a large rotating gas cloud. As the gas falls into the black hole, it is heated to millions of degrees. The heated gas emits thermal radiation; this spans the spectrum, making the quasar the brightest in the visible spectrum and x rays.

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